This tutorial will introduce you to the topics and content available on the DOSITS web site involving the effects of underwater sound on marine animals. It is suitable for the general public. Advanced science content is available throughout the site. Please refer to Advanced Topics in the main site navigation bar.
Sounds produced by marine animals, natural processes, and human activities fill the ocean. Because water is an effective medium for the transmission of sound, both marine animals and people use sound as a tool for finding objects, navigating, and communicating under water. Underwater sound allows marine animals to gather information and communicate at great distances and from all directions. Many marine animals rely on sound for survival and depend on adaptations that enable them to acoustically sense their surroundings, communicate, locate food, and protect themselves under water.
Research suggests that increased background noise and specific sound sources might impact marine animals in several ways. The potential impacts include sounds that cause marine animals to alter their behavior, prevent marine animals from hearing important sounds (masking), cause hearing loss (temporary or permanent), or damage tissue. In at least three well-documented cases there is a relationship in time and space between the use of mid-frequency sonar and the stranding of cetaceans, mostly beaked whales. To put this in context, the total number of stranded whales associated with sonar use, at least 40, can be compared with the average number of whale strandings per year, 3,600 in the United States alone. This can also be compared with the number of marine mammal deaths per year associated with fisheries bycatch, estimated to be 650,000 animals globally (Read et al., 2006).
The process for considering if and how much a sound source is likely to affect marine animals is called ecological risk assessment. The first step of this scientific process is to identify the problem. The next stage involves estimating the probability of being exposed to the problem and, based on that exposure, determining the types of ecological effects that are expected. Then the risk can be estimated.
Actions may then be taken to reduce effects on marine life. Federal laws such as the Endangered Species Act, Marine Mammal Protection Act, and National Environmental Policy Act that aim to protect animals from harassment (including impacts from sound sources) have motivated studies of marine animals and the development of mitigation techniques and alternate technologies. The extent to which many commonly used mitigation measures are effective has not been determined.